From 5db1765bee29f7f55fadba52ee86cf8f59583b3a Mon Sep 17 00:00:00 2001
From: "N. Engelhardt" <nak@yosyshq.com>
Date: Thu, 17 Apr 2025 18:17:42 +0200
Subject: [PATCH] add flatten -nocleanup option

---
 passes/techmap/flatten.cc | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/passes/techmap/flatten.cc b/passes/techmap/flatten.cc
index 3425509b1..6363b3432 100644
--- a/passes/techmap/flatten.cc
+++ b/passes/techmap/flatten.cc
@@ -349,6 +349,10 @@ struct FlattenPass : public Pass {
 		log("    -separator <char>\n");
 		log("        Use this separator char instead of '.' when concatenating design levels.\n");
 		log("\n");
+		log("    -nocleanup\n");
+		log("        Don't remove unused submodules, leave a flattened version of each\n");
+		log("        submodule in the design.\n");
+		log("\n");
 	}
 	void execute(std::vector<std::string> args, RTLIL::Design *design) override
 	{
@@ -360,6 +364,8 @@ struct FlattenPass : public Pass {
 		if (design->scratchpad.count("flatten.separator"))
 			worker.separator = design->scratchpad_get_string("flatten.separator");
 
+		bool cleanup = true;
+
 		size_t argidx;
 		for (argidx = 1; argidx < args.size(); argidx++) {
 			if (args[argidx] == "-wb") {
@@ -378,6 +384,10 @@ struct FlattenPass : public Pass {
 				worker.separator = args[++argidx];
 				continue;
 			}
+			if (args[argidx] == "-nocleanup") {
+				cleanup = false;
+				continue;
+			}
 			break;
 		}
 		extra_args(args, argidx, design);
@@ -414,7 +424,7 @@ struct FlattenPass : public Pass {
 		for (auto module : topo_modules.sorted)
 			worker.flatten_module(design, module, used_modules, worker.separator);
 
-		if (top != nullptr)
+		if (cleanup && top != nullptr)
 			for (auto module : design->modules().to_vector())
 				if (!used_modules[module] && !module->get_blackbox_attribute(worker.ignore_wb)) {
 					log("Deleting now unused module %s.\n", log_id(module));